Spark plug



R. J. LUKEMAN May 3, 1949.

Filed Jan. 10, 1947 mvaa'roa RICHARD-Jima AN W l/n A-rronNeY `lfatented May 3, 1949 UNITED 'srArEs PATENT OFFICE srmx PLUG i i Richard J. Lukeman, Montreal, Quebec, Canada pp'iieauon January 10, 1947, serial No, 721,359

. 1 Claim. 1

This invention 'relates to improvements in spark pluss- The principal object of the .i'nvention 'is the provision of a multiple gap spark plug in which spark gaps of difierent predetermined lengths are provided by an arrangement of sparking points which lhas the effect of confining arcing of the current to that gap whose length is best suited to the compression of the engine cylinder in which the spark plug is tted. More particularly, the invention consists in the provision of a spark plug including a single insulated electrode having branch terminals afiording a plurality of sparking points arranged to provide, in conjunction with a single grounded electrode, a plurality of spark gaps of different predetermined lengths. The varying lengths of the spark gap are preselected to give a plurality of different spark gap settings each adapted to suit a particular cylinder compression.- For example, in a three gap spark plug embodying the invention one gap may have a setting of .025 to suit the cylinder compression of the engine of a Dodge motor vehicle; another gap may have a setting of .030 to suit the cylinder compression of the engine'in the Hudson and other types of automobiles; and thethird gap may have a setting of .039 to suit the cylinder compression of Chevrolet and other similar automobile engines.

Proceeding now to a more detailed discussion of the inventicn reference will be had to the accompan'ying drawings, Wherein- Fig. 1 is a fragmentary longitudinal sectional view of the lower portion of a spark plug embodying my invention; and

Fig. 2 is a sectional view taken substantially along the section line 2 2 of F'ig. 1.

In the drawings, I have shown only the lower portions of the shell 5 and insulator 6 of a spark plug embodying my invention since these shell and insulator elements may be of any suitable design and assembled in conventional manner.

A central insulated or positive electrode 1 is cemented or otherwise permanently secured in the insulator and a ccoperating grounded or negative electrode 8 is secured to the bottom of the metal Shell ti.

The insulated electrode 'i extends through the insulator E1 in the usual manner and may be fitted, at its upper end, with the usual binding post arrangement. The lowerend of electrode 'l :is branched to provide three sparking points or i terminals designated 9, ll) and I i. In the present instance these terminals are shown lyi'ng in a common planc with the terminals 9 and II lying at opposite sides of and projecting beyond the central terminal IO.

The grounded terminal 8 is shown as an L-shaped terminal presenting a Vertical limb 8a attached to shell 5 and a horlzontal limb 8b which is positioned between and in spaced relation to the lower extremities of the terminals or sparking points 9 and II. The horizontal limb 8b of electrode 8 is also positioned so that it provides, in conjunction with the terminals or Sparking points 9, I' and Il, three spark gaps A, B and C of different predetermined lengths. In this connection it will be noted that the gap A is shorter than the gap B and that the latter is shorter than the gap C, thereby giving three different spark gap settings each of which is predetermined to suit a particular cylinder compression.

When the spark plug described hereln is in use the arcing of the current which produces the fuel igniting spark is apparently confined to that particular gap whose Vlength is best suited to the compression of the cylinder in which the sparh plug is tted.

I am aware that it has been previously proposed to provide the metal shell or casing of a sparlz; plug with a plurality of grounded electrodes serving, in conjunction with a single insulated electrode, to provide a plurality of spark gaps but such an arrangement does not have the same effect as that provided for by my invention in which a single electrode on the shell or casing of the plug cooperates with three .terminal branches of a single insulated electrode to provide a plurality of sparl; gaps each of a different predetermined length. My improved spark plug also diifers in function and efiect from those spark plugs in which a plurality of separate electrodes are secured in the insulator to cooperate with a single electrode on the shell or casing.

I-Iaving thus described the nature of my invention and a preferred embodiment thereof, it will be understood that various modifications may be resorted to within the scope and spirit of the invention as defined by the appended claim.

I claim:

A multiple spark gap sparl: plug in which sparh gaps of different predetermined lengths are provided by an arrangement of sparking terminala which has the effect of confining arcing of the current to that gap whose length is best suited to the compression of the engine cylinder in which the spark plug is fitted, said plug comprising a metal shell, an insulator fitted in said shell, a central insulated electrode extending downwardly through said insulator and said shell, the lower end of said electrode being branched to provide three terminals including two outer laterally spaced terminals of substantially equal length and a central terminal of shorter length located between said outer terminals, and a grounded electrode having one end secured to said shell and the other end interposed between the outer terminals of the insulated electrode in spaced relation thereto, said grounded electrode being also positioned below and in spaced relation to the central terminal of said insulated electrode, the relative arrangement of the grounded electrode and the terminals of the insulated electrode being such that the length of the spark gap between the grounded electrode and any. one terminal of the insulated electrode is different from the length 'el of the gap separating the grounded electrode from any one of the remeining terminale o! the insulated electrode.

RICHARD J. LUKEMAN.

REFERENCES CITED The following references are of record in the file of. this patent:

UNITED s'm'ms PATENTS Watts Mar. 27, 133% 

